ABSTRACT Staphylococcus aureus (SA) is a major cause of cutaneous infections. Virulent community-acquired methicillin-resistant SA (MRSA) is the most common source of skin and soft tissue infections in U.S. hospitals. Prompt recruitment of polymorphonuclear (PMN) leukocytes in sufficient numbers to the site of infection is critical for controlling MRSA infection and preventing dissemination to vital organs. Unexpectedly, we recently discovered that hematopoietic stem and progenitor cells (HSPCs) are also recruited to wounds, and these cells detect bacterial antigens and virulence factors, and augment PMN numbers necessary to resolve a MRSA infected wound. The signaling process eliciting an increase in myeloid recruitment and differentiation of HSPC within the wound was found to involve toll-like receptor 2 (TLR2) detection of peptidoglycans derived from the gram-positive cell wall and released within the wound. We propose that this newly discovered host immune trait is an adaption to effectively overcome immune suppression by MRSA virulence factors such as ?-hemolysin toxin (AT) that blocks PMN recruitment by lysing perivascular macrophages that help guide them to sites of infection. The central hypothesis governing this proposal is that immune-modulation that tunes PMN number and antibacterial activity against MRSA infection can hasten clearance and healing. This proposal will utilize our innovative model of wound infection that employs genetically-engineered bioluminescent bacteria and a transgenic lysozyme- M-EGFP knock-in mouse that produces fluorescent mature PMN. This model will be used in conjunction with advanced in vivo whole animal optical imaging to noninvasively and longitudinally monitor bacterial burden and immune responses. A translational goal will be the implementation of human CD34+ HSPC myeloid expansion to evaluate the therapeutic potential of local PMN expansion to combat MRSA infection in an immunodeficient (NSG) mouse wound model.